SMSL D400 MK2 adds XMOS XU-316 processing and five dual op-amps

The SMSL D400 MK2 is a high-performance desktop DAC built around AKM’s flagship AK4191 digital processing stage and AK4499EX conversion architecture, with third-generation XMOS XU-316 USB processing, a ±5 ppb 10 MHz OCXO clock, and five dual op-amps in the analog stage. It supports PCM up to 32-bit/768 kHz, native DSD512, MQA and MQA-CD decoding, and LDAC Bluetooth playback up to 24-bit/96 kHz. Balanced XLR and single-ended RCA outputs allow the D400 MK2 to feed headphone amplifiers, preamplifiers, integrated amplifiers, and other downstream audio components.

AK4191 and AK4499EX conversion architecture

The D400 MK2 separates digital processing and digital-to-analog conversion between AKM’s AK4191 and AK4499EX. This architecture places the digital filtering and processing functions in the AK4191 while the AK4499EX handles the analog conversion stage, providing a dedicated signal path for high-resolution PCM and DSD sources.

Measured through the balanced outputs, dynamic range and signal-to-noise ratio both reach 132 dB, with THD+N rated at 0.00006% (-124 dB, unweighted). RCA performance reaches 126 dB for both dynamic range and SNR, with THD+N of 0.00008% (-121 dB, unweighted). The XLR outputs operate at 5 Vrms with a 200-ohm output impedance, while RCA provides 2.5 Vrms at 100 ohms.

XMOS XU-316 handles high-resolution USB and I²S

A third-generation XMOS XU-316 processor manages high-bandwidth digital input over USB and I²S. Both interfaces support PCM from 44.1 kHz through 768 kHz at 16- to 32-bit resolution, along with 1-bit DSD from 2.8224 MHz through 22.5792 MHz, including native DSD512. USB transmission is asynchronous, allowing the D400 MK2 to control audio timing rather than relying on the source computer’s USB clock.

Optical and coaxial inputs support PCM from 44.1 kHz through 192 kHz at up to 24-bit resolution, as well as DoP64 for DSD-over-PCM transmission. A dedicated DoP indicator identifies compatible DSD-over-PCM signals when they are received.

10 MHz OCXO and CK-04 clock processing

Digital timing is referenced to a built-in 10 MHz oven-controlled crystal oscillator specified at ±5 ppb. An OCXO maintains the crystal at a controlled operating temperature to reduce frequency variation, providing the conversion circuitry with a stable timing reference.

SMSL also incorporates its CK-04 clock processing circuit to manage timing jitter before digital-to-analog conversion. Keeping clock variation low reduces timing error in the sampled signal and supports consistent conversion across the D400 MK2’s supported digital interfaces.

MQA, MQA-CD, and multiple digital input formats

The D400 MK2 provides hardware MQA decoding through USB, optical, and coaxial inputs, along with MQA-CD support. Compatible encoded material can therefore be decoded within the DAC rather than depending entirely on upstream software processing.

Its wired digital inputs include USB, optical, coaxial, AES/EBU, and I²S, covering computers, disc transports, dedicated streamers, and other digital sources. I²S also supports native DSD transmission for compatible source components.

LDAC and aptX HD Bluetooth playback

A Qualcomm Bluetooth platform adds wireless playback through LDAC, aptX HD, aptX, SBC, and AAC. LDAC supports up to 24-bit/96 kHz transmission at 990, 660, or 330 kbps, while aptX HD operates at up to 24-bit/48 kHz and 576 kbps. Standard aptX, SBC, and AAC provide additional compatibility with phones, tablets, computers, and streamers that do not support the higher-bandwidth codecs.

Bluetooth functions as another selectable digital source rather than replacing the higher-bandwidth USB and I²S paths, allowing the same DAC and analog output circuitry to serve both wireless and wired playback.

Five dual op-amps and independent power regulation

Five high-grade dual op-amps are used in the D400 MK2’s analog circuitry. The DAC, op-amp, digital, and analog sections receive independent low-noise voltage regulation, reducing electrical interaction between circuit stages and maintaining separate supply conditions for processing and analog output functions.

The completed analog signal is available simultaneously through balanced XLR and single-ended RCA connections. The specified 5 Vrms balanced and 2.5 Vrms single-ended output levels provide standard line-level connections for downstream headphone amplifiers, preamplifiers, and integrated amplifiers.

Machined aluminum chassis and color display

The D400 MK2 is housed in a CNC-machined aluminum-alloy enclosure. Its all-metal construction provides physical rigidity and electromagnetic shielding around the internal digital, clock, power, and analog circuitry.

A fully laminated IPS color display presents input, decoding, and operating information behind tempered glass. Front-panel control is handled through a multifunction knob, while the supplied infrared remote provides power, navigation, input selection, mute, programmable FN control, and volume adjustment. Rear-panel connectors use gold-plated terminals for oxidation resistance and consistent electrical contact over repeated connections.

System compatibility and operating specifications

The D400 MK2 supports Windows 7, 8, 8.1, 10, and 11 with the appropriate driver, macOS 10.6 or later, and driverless operation under Linux. Power consumption is rated below 10 W, with standby consumption below 0.5 W. The chassis measures 10 × 7.44 × 1.81 inches (254 × 189 × 46 mm) and weighs 4.18 lb (1.9 kg).

Availability

The SMSL D400 MK2 is available now at Apos.